The present invention relates to a semiconductor integrated circuit device and the manufacture thereof; and, more specifically, the invention relates to a technology which is applicable to a semiconductor integrated circuit device comprising a silicon oxynitride film used as a gate insulating film for a MISFET (Metal Insulator Semiconductor Field Effect Transistor).
To realize a low-voltage operation of a MISFET, the gate oxide film thereof must be made thinner in proportion to a reduction in the thickness of the MISFET. However, when the thickness of the gate oxide film is reduced, a direct tunnel current running through the film grows, thereby causing a gate leakage current, which cannot be ignored from the viewpoint of reducing the power consumption.
To cope with this problem, attempts have been made to increase the physical thickness of the gate insulating film by using a high dielectric film, such as a titanium oxide (TiO2) or tantalum oxide (Ta2O5) film, having a higher relative dielectric constant than silicon oxide. However, since the gate insulating film that is formed of this high dielectric film has many problems with interfacial control and the like, use of this film in mass-produced devices is currently considered to be difficult.
Since a silicon oxynitride film that is formed by nitriding part of a silicon oxide film has a higher dielectric constant than silicon oxide, the effect of reducing the leakage current by increasing the physical thickness of a gate insulating film can be expected from this film. It is reported that a gate insulating film formed of a silicon oxynitride film is effective in achieving a suppression of boron leakage in which an impurity (boron) contained in a p type gate electrode goes through the channel area of a substrate at the time of heat treatment during the process, an improvement of the hot carrier resistance of the MISFET and an improvement of the electron mobility of an n channel type MISFET.
As a means of nitriding a gate insulating film made from silicon oxide, there is a known method in which a substrate is heated in a high-temperature atmosphere of around 1,000xc2x0 C. containing an NO (nitrogen monoxide) gas after a silicon oxide film is formed on the silicon substrate.
Japanese Unexamined Patent Publication No. 2001-332724 discloses a technology for forming a gate insulating film from silicon oxynitride having two peaks of nitrogen concentration at the interface with a silicon substrate and in the film, to prevent the penetration of boron contained in the p type gate electrode and to improve hot carrier resistance, in an MIS device having a so-called dual gate structure using an n type gate electrode as an n channel MISFET and a p type gate electrode as a p channel MISFET.
To form the above-described silicon oxynitride film, a silicon substrate is first wet oxidized to form a silicon oxide film having a thickness of about 7 nm on the surface; it is then heated in an atmosphere containing an NO gas to segregate nitrogen at the interface between the silicon oxide film and the substrate; and then it is dry oxidized. When this dry oxidation is carried out, the interface between the silicon oxide film and the substrate is oxidized to form a silicon oxide film having a thickness of 1 to 2 nm underlying an area where nitrogen has been segregated. Thereafter, when the substrate is heated in an atmosphere containing an NO gas again, nitrogen is segregated at the interface between the silicon oxide film underlying the area where nitrogen has been segregated and the substrate, thereby obtaining a gate insulating film made of silicon oxynitride and having two peaks of nitrogen concentration at the interface with the silicon substrate and in the film.
Japanese Unexamined Patent Publication No. 2000-357688 discloses a technology for forming a gate insulating film from silicon oxynitride having two peaks in the nitrogen concentration distribution in the thickness direction by a method different from that of the above-referenced publication.
In this publication, the silicon substrate is first heated in an oxygen atmosphere to form a silicon oxide film having a thickness of about 5 nm on the surface, and then it is heated in an NO gas atmosphere to form a silicon oxynitride film having a thickness of about 5.5 nm having a peak of nitrogen concentration near the interface with the substrate. Thereafter, the surface of this silicon oxynitride film is etched with a hydrofluoric acid aqueous solution to remove its surface layer portion, thereby obtaining a silicon oxynitride film having a thickness of about 1 nm and containing nitrogen in the entire thickness direction in large quantities. Thereafter, a second heat treatment is carried out in an NO gas or N2O gas atmosphere to grow a new thermally oxidized film on the substrate and introduce nitrogen into the thermally oxidized film, thereby obtaining a silicon oxynitride film having two peaks in nitrogen concentration distribution in the thickness direction.
Japanese Unexamined Patent Publication No. Hei 8(1996)-167664 (U.S. Pat. No. 5,591,681) discloses a technology for forming a silicon oxide film containing nitrogen by heating in a NO or N2O gas atmosphere.
When the above-described silicon oxynitride film is used as a gate insulating film for a MISFET and the gate insulating film becomes thinner in proportion to a reduction in the thickness of the MISFET, the dielectric constant must be increased by raising the concentration of nitrogen contained in the film in order to reduce the gate leakage current.
However, it is difficult to increase the dielectric constant of the silicon oxynitride film, formed by the conventional oxynitridation treatment in which nitrogen is introduced into a silicon nitride film by heating a substrate in a NO to gas or N2O gas atmosphere, by increasing the concentration of nitrogen contained in the entire film, because the surface of the film is not nitrided, although the concentration of nitrogen near the interface between the film and the substrate can be increased.
When a portion near the interface between the gate insulating film and the substrate is nitrided excessively, a trap in the interfacial level or the film increases, thereby causing a problem, such as a reduction in the carrier mobility of the MISFET.
FIG. 30 is a graph showing the relationship between the concentration of nitrogen at the interface between the gate insulating film and the substrate and the carrier mobility of a MISFET. As shown in the graph, in the case of an n channel MISFET in which electrons are carriers, when several atomic percents of nitrogen is introduced into the interface, the carrier mobility becomes higher than when nitrogen is not introduced, but when the concentration of nitrogen further increases, the above effect gradually decreases. Meanwhile, in the case of a p channel MISFET in which electron holes are carriers, the carrier mobility becomes lower in proportion to the concentration of nitrogen at the interface. When the concentration of nitrogen is higher than 10 atomic %, the carrier mobility drops by about 20%, thereby reducing the drain current (Ids) by about 10% and making circuit design difficult to achieve in practice.
Thus, the method of introducing nitrogen into a silicon oxide film by oxynitridation treatment has limits in the amount of introduced nitrogen.
In the above-described technology for forming a silicon oxynitride film having two peaks in the nitrogen concentration distribution in the thickness direction, the high-temperature oxynitridation treatment is carried out several times, with the result that the silicon oxynitride film becomes thick, thereby making it difficult to form a gate insulating film as thin as 5 nm or less.
It is an object of the present invention to provide a technology that is capable of forming a silicon oxynitride film having a high concentration of nitrogen in a semiconductor integrated circuit device comprising a silicon oxynitride film used a gate insulating film for a MISFET
It is another object of the present invention to provide a technology that is capable of improving the reliability of a semiconductor integrated circuit device comprising a silicon oxynitride film used as a gate-insulating film for a MISFET.
The above and other objects and new features of the present invention will become apparent from the following description and the accompanying drawings.
The present invention relates to the following.
The method of manufacturing a semiconductor integrated circuit device according to the present invention comprises the following steps:
(a) forming a silicon oxide gate insulating film on a main surface of a semiconductor substrate made from monocrystal silicon by heating the semiconductor substrate,
(b) introducing nitrogen into the gate insulating film by heating the semiconductor substrate in an atmosphere containing an NO gas or N2O gas;
(c) introducing nitrogen into the gate insulating film by exposing the semiconductor substrate to a nitrogen plasma atmosphere; and
(d) forming gate electrodes for a MISFET over the gate insulating film after the steps (b) and (c).
According to the above method, since a gate insulating film can be formed from silicon oxynitride by using both an oxynitridation treatment and a nitrogen plasma treatment, the concentration of nitrogen contained in the gate insulating film can be increased without raising the concentration of nitrogen near the interface between the substrate and the gate insulating film to a higher level than required.
According to a first aspect of the present invention, there is provided a semiconductor integrated circuit device comprising MISFET""s having a 5 nm or less-thick gate insulating film formed from silicon oxynitride on the main surface of a semiconductor substrate made from monocrystal silicon, wherein nitrogen contained in the gate insulating film has a first peak concentration near the interface between the: semiconductor substrate and the gate insulating film and a second peak concentration near the surface of the gate insulating film.
According to a second aspect of the present invention, there is provided a semiconductor integrated circuit device wherein the second peak concentration is higher than the first peak concentration.
According to a third aspect of the present invention, there is provided a semiconductor integrated circuit device wherein the MISFET""s have a gate electrode containing a silicon film doped with boron.
According to a fourth aspect of the present invention, there is provided a semiconductor integrated circuit device wherein the first peak concentration is in the range of 1 to 10 atomic %.
According to a fifth aspect of the present invention, there is provided a semiconductor integrated circuit device comprising MISFET""s having a 5 nm or less-thick gate insulating film formed of a laminate consisting of a silicon oxynitride film and a silicon nitride film formed over the silicon oxynitride film on the main surface of a semiconductor substrate made from monocrystal silicon, wherein the concentration of nitrogen contained in the silicon oxynitride film is the highest near the interface between the semiconductor substrate and the silicon oxynitride film.
According to a sixth aspect of the present invention, there is provided a semiconductor integrated circuit device wherein the MISFET""s have a gate electrode containing a silicon film doped with boron.
According to a seventh aspect of the present invention, a semiconductor integrated circuit device is provided wherein the concentration of nitrogen contained near the interface between the semiconductor substrate and the silicon oxynitride film is in the range of 1 to 10 atomic %.